Recently, discussion of a new radio access technology (NR) or a 5th generation (5G) system, which is a next generation communication system after long term evolution (LTE) (or evolved universal terrestrial radio access (E-UTRA)) and LTE-advanced (LTE-A) (or E-UTRA Evolution), is actively conducted to process exclusively increasing mobile data traffic. When compared to a legacy mobile communication system that focuses on a common voice/data communication, the 5G system is aimed at satisfying various services, such as an enhanced mobile broad-band (eMBB) service for enhancing an existing voice/data communication, an ultra-reliable and low latency communications (URLLC) service, a massive machine-type communications (mMTC) service for supporting massive machine-to-machine communication, and the like, and various requirements associated with each service.
In order to meet the wireless data traffic demand that has been increasing after the popularization of the 4G communication system, efforts to develop an improved 5G communication system or a pre-5G communication system are being made. For this reason, the 5G communication system or the pre-5G communication system is called a beyond 4G network communication system or a post LTE system. In order to achieve a high data transmission rate, the implementation of the 5G communication system in an ultrahigh frequency (mmWave) band (e.g., 60 GHz band) is being considered. To reduce the path loss of a radio wave signal in the ultrahigh frequency band and to increase the transmission distance of a radio wave signal, the 5G communication system has been discussing beamforming using an array antenna, massive MIMO, full dimensional MIMO (FD-MIMO), hybrid beamforming, and large scale antenna technologies. Further, the 5G communication system has been developing technologies, such as an evolved small cell, an advanced small cell, a cloud radio access network (RAN), an ultra-dense network, device to device communication (D2D), a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMP), received interference cancellation, and the like, in order to improve the system network. In addition, the 5G system has been developing hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC) and non-orthogonal multiple access (NOMA), which are advanced access technologies.
Meanwhile, the Internet has been evolved to the Internet of Things (IoT) network that exchanges and process information between distributed components such as objects and the like in a human-oriented connection network in which humans generate and consume information. An Internet of Everything (IoE) technology in which a big data processing technology through a connection with a cloud server or the like is combined with the IoT technology has emerged. In order to implement IoT, technical factors such as a sensing technology, wired/wireless communication, network infrastructure, service interface technology, and security technology are required, and thus, technologies such as a sensor network, machine to machine (M2M), machine type communication (MTC), and the like for a connection between objects are recently being researched. In an IoT environment, through the collection and analysis of data generated from connected objects, an intelligent Internet Technology (IT) service to create a new value for the human's life may be provided. IoT may be applied to fields, such as a smart home, a smart building, a smart city, a smart car or connected car, a smart grid, healthcare, smart home appliance, or high-tech medical service, through the convergence of the conventional Information Technology (IT) and various industries.
Accordingly, various attempts to apply the 5G communication system to an IoT network are being made. For example, 5G communication technologies such as a sensor network, M2M communication, and MTC are implemented by schemes such as beamforming, MIMO, and array antenna. The application of a cloud RAN as the big data processing technology may be an example of the convergence of the 5G technology and the IoT technology.
An OFDM scheme can maintain orthogonality between subcarrier symbols while overlapping subcarrier spectrums, and is a transmission technology that is capable of applying a multi-antenna transmission/reception scheme for each subcarrier in the frequency domain even in a multi-path padding wireless channel environment by using a few time overheads, such as a cyclic prefix (CP). When compared to other multi-carrier technologies, the OFDM scheme is capable of increasing frequency efficiency with low complexity, which is an advantage. The OFDM scheme is widely used as a wireless standard technology in a Wi-Fi system, an LTE system that is the 4th generation wireless communication system, or the like, and will be utilized as a baseline waveform for a band that is less than or equal to 40 GHz in a 5th generation wireless communication system standardization process of 3GPP. Also, the OFDM scheme is capable of grouping a plurality of subcarriers and allocating resources to a plurality of users in a single symbol with low interference, and thus, may be utilized as a multi-access scheme called orthogonal frequency division multiple access (OFDMA).
However, the OFDM scheme belongs to a multi-carrier technology, and thus, it is formed as the sum of a plurality of subcarrier symbols having different phases in the time domain and has a high PAPR or cubic metric (CM) feature. Therefore, it is difficult to effectively use a power amplifier in the OFDM scheme. Particularly, in the case of the OFDM-based uplink transmission, the efficiency of a power amplifier of a terminal may largely affect battery power consumption. Accordingly, an LTE system of 3rd generation partnership project (3GPP) employs DFT-spread OFDM (DFT-S-OFDM) as an uplink transmission technology. The DFT-S-OFDM is a spreading transmission scheme based on discrete Fourier transform (DFT), which is well known by the name of single carrier frequency division multiple access (SC-FDMA) in an LTE system of the 3rd generation partnership project. In comparison with the OFDMA scheme, the DFT-S-OFDM can perform transmission with a relatively 2 to 3 dB lower PAPR and thus, may increase the efficiency of a power amplifier of a terminal.
However, in the case of the DFT-S-OFDM, the size of a spreader is smaller than the size of an inverse fast Fourier transform (IFFT) of the OFDM scheme, and an uplink resource is allocated in many cases. Also, due to multi-user channel estimation, scheduling performance, and the like, a single terminal signal is transmitted based on a subband unit of consecutive subcarriers. The LTE system is also designed to use a localized DFT-S-OFDM transmission architecture in an uplink. In this instance, a PAPR (6 dB or more) still has a drawback worse than a PAPR (2 to 4 dB) of a preamble (e.g., uplink demodulation reference signal (UL DM-RS) of an LTE system) for uplink channel estimation.
Around 2005, a “frequency domain spectral shaping” scheme that is capable of lowering a PAPR by applying a pulse such as a root raised cosine (RRC), instead of a sinc pulse that is applied to the DFT-S-OFDM, was proposed (NTT DoCoMo, NEC, and SHARP, “R1-050702: DFT-spread OFDM with Pulse Shaping Filter in Frequency Domain in Evolved UTRA Uplink,” 3GPP TSG RAN WG1, meeting 42, London, UK, August 2005). In the present specification, to clearly express the “frequency domain spectral shaping” scheme from the perspective of function, it is called circular filter spreading OFDM (CFS-OFDM).
Also, although the 5th generation mobile communication standardization process of 3GPP has considered OFDM as an uplink/downlink common waveform, a similar spreading OFDM scheme, such as DFT-S-OFDM and CFS-OFDM, is additionally considered as an uplink waveform for coverage enhancement. A PAPR may be a great influential factor for determining an amount of back-off when a power amplifier (PA) is designed. Therefore, when the PAPR is dramatically lowered to the level of a single-tone transmission, the cost of mounting a PA may be reduced or PA efficiency may be increased, and thus, it may be helpful for a low-power operation of a terminal of which battery consumption is a big issue. Alternatively, although a low PAPR signal is transmitted at a larger transmission power in comparison with a higher PAPR signal, in the same PA, signal distortion may be low and thus, it may be helpful for cell coverage enhancement.
A PAPR is an important yield for determining a driving power of a terminal. When the PAPR is significantly high, battery is consumed quickly, and thus, user experience may be lowered. The CFS-OFDM may raise a PAPR performance by sacrificing a small amount of resource in a technology such as an Internet of things (IoT) of which a transmission rate is relatively less important, and enables a terminal existing in an edge area of a cell to perform effective uplink transmission. However, an RRC filter proposed in the existing CFS-OFDM satisfies an orthogonal condition but has difficulty in providing an optimal transmit waveform that is designed from the perspective of a PAPR.